fix panic when `Iterate()` fails (#2040)

not to call `rows.Err()`

Reviewed-on: https://gitea.com/xorm/xorm/pulls/2040
Reviewed-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: daisuzu <daisuzu@noreply.gitea.io>
Co-committed-by: daisuzu <daisuzu@noreply.gitea.io>

rows.go

@@ -140,5 +140,5 @@ func (rows *Rows) Close() error {
 		return rows.rows.Close()
 	}
 
-	return rows.Err()
+	return nil
 }